Solved Page showing in background before main site loads!!

Hi there, am new here and learning lots about my website (how to update it etc) I have done heaps of work on it this week including upadting the theme in customiser and setting up a new template for Posts. It seems since I have made all the changes everytime I refresh the page then another version flashes up in the background for a second before the page loads - how do I stop this? I asked my website host and they thought it was a caching issue but they sorted that and it still happens so they suggested the forum - would it be to do with Child themes? Any help greatly appreciated - I am a basic website admin person so need really basic instructions haha!

 

Thank you so much, it looks like this worked perfectly! Really appreciate your help yay!